Testcomplete to handle username and password when the password change is required

There are several ways you can do this. I would recommend storing the credentials somewhere all projects / suites can access them by creating a shared login utility so you only have to update in one place.

If your tests are all performing the same steps when logging in, that process should not be recreated for each test, that creates a maintenance night-mare, not only for the credentials like you are seeing, but especially if the login process ever changes. 

If you create a shared script or keyword test you will only ever have to make a change once, as opposed to however many different tests are logging into the AUT.